Electric machines are utilized in a wide variety of applications. For example, hybrid/electric vehicles (HEVs) typically include an electric traction drive system that includes an alternating current (AC) electric motor which is driven by a power converter with a direct current (DC) power source, such as a storage battery. Motor windings of the AC electric motor can be coupled to inverter sub-modules of a power inverter module (PIM). Each inverter sub-module includes a pair of switches that switch in a complementary manner to perform a rapid switching function to convert the DC power to AC power. This AC power drives the AC electric motor, which in turn drives a shaft of HEV's drivetrain. Traditional HEVs implement two three-phase pulse width modulated (PWM) inverter modules and two three-phase AC machines (e.g., AC motors) each being driven by a corresponding one of the three-phase PWM inverter modules that it is coupled to.
Many modern high performance AC motor drives use the principle of field oriented control (FOC) or “vector” control to control operation of the AC electric motor. In particular, vector control is often used in variable frequency drives to control the torque applied to the shaft (and thus finally the speed) of an AC electric motor by controlling the current fed to the AC electric motor. In short, stator phase currents are measured and converted into a corresponding complex space vector. This current vector is then transformed to a coordinate system rotating with the rotor of the AC electric motor.
Recently, researchers have investigated the possibility of using multi-phase machines in various applications including electric vehicles. As used herein, the term “multi-phase” refers to more than three-phases, and can be used to refer to electric machines that have three or more phases. One example of a multi-phase electric machine is a five-phase AC machine. In a five-phase system, a five-phase PWM inverter module drives one or more five-phase AC machine(s).
While the possibility of using five-phase systems (e.g., five-phase inverter and motor configurations) in HEVs is being explored, a lot of work remains to be done before these systems can actually be implemented. For instance, in the context of five-phase electrical drives implemented in an HEV, high torque for any given rotation speed is desirable since the maximum torque available allows faster acceleration and deceleration of the HEV, and for better dynamic performance during driving.
Accordingly, it is desirable to increase output voltage generated by the inverter module that drives a five-phase AC machine since this increases mechanical torque generated by the five-phase machine, which can improve machine efficiency and performance, as well as utilization of the DC voltage source. Other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background